ABSTRACT: A three year study is proposed to develop a canine model to determine angiographic, hemodynamic and pathologic correlates of critical versus non-critical coronary artery narrowings. This study is sponsored under the auspices of Divisions of Cardiology and Cardiothoracic Surgery. Unlike previous studies, we will use reduction of flow as the basis of our definition of what constitutes a critical lesion both at rest and high flow states. Coronary artery constrictions will be made surgically by placing occluders of known dimensions around a given coronary artery. The impact of critical and non-critical native coronary artery lesions proximal to the area of graft implant on coronary artery bypass graft flow will also be determined. A comparison will be made between the angiographic appearance of these coronary artery constrictions and those observed during detailed postmortem examinations of the animals. Furthermore in addition to reduction of flow, those parameters that determine patency of the coronary artery bypass graft will be investigated, such as the geometry of the graft-artery combination, velocity of flow in the bypass graft, and the differences in the mechanical properties of the bypass graft and native coronary artery. All dogs will be followed on a chronic basis to determine long-term graft patency and the effect of collaterals on graft patency. A comparison will be made between the results obtained from this proposed study and an existing study currently being undertaken that is investigating pulsatile flow in artificial compliant arteries. This in vitro program is currently determining the factors that increased turbulence and shear stress patterns under laborabory conditions at the bifurcation of a simulated bypass graft and native coronary artery.